Yikes!
You're really resisting the idea that you've got this all wrong, aren't you?
I wasn't born in the US, and I'm not American, but I've lived there for a few decades, which is why I know a lot more about America and Americans than you do.
The American social whirl exists without any reference to what is generally considered either very quaint (British) or very chic but inexplicably and suspiciously socialist (French/ Italian/ Scandinavian) societies and their norms.
Hence occasions like the Met Gala, but also big dos and galas in pretty much every city that boasts an art museum or a children's hospital or a conservatory of music or an opera house, ballet, or orchestra, etc - a lot of cities, in other words. Off the top of my head, I can think of at least eight gala events coming up over the winter in the city where I live, all of which offer the chance to wine and dine and dance the night away in the company of locally and nationally known luminaries if you care to fork over the price of a ticket.
Here's what's going on in Dallas this Autumn:
dallas.culturemap.com/news/society/dallas-galas-crystal-cattle-two/
A 'power lunch' in NYC that raised $1.5m for meals on wheels:
www.newyorksocialdiary.com/citymeals-on-wheels-raised-1-5-million-at-its-37th-annual-power-lunch/
'Young Professionals' opportunities for networking/ organising events in Chicago:
better.net/money/career/11-best-young-professionals-groups-in-chicago/
Various charity galas around the US:
better.net/philanthropy/get-involved/the-biggest-charity-galas-to-attend-all-year-round-2/
Obviously that's just a snapshot, involving only charity galas, and only a few cities.
Half British Apple Martin will probably spend her next ten years attending parties, galas, launch parties, society weddings, and other events where there are photographers. The Bal is one event among hundreds she'll clock up, the vast majority of which will be in the US, and she'll meet the same jet set crowd she danced with at the Bal at many events. As noted, she's off to a good start by pledging Kappa Kappa Gamma.